Tunable coupling circuit arrangement for ultra-short waves



Jan. 30, 1940. K. SCHLESINGER 2,188,486

TUNABLE COUPLING CIRCUIT ARRANGEMENT FOR ULTRA-SHORT WAVES Filed Feb. 19, 1938 J27 venf0r= Patented Jan. 30, 1940 TUNABLE' COUPLING CIRCUIT "ARRANGE- MENT FOR ULTRA-SHORT WAVES 'Kurt Schlesinger, Berlin, Germamgassignor, by mesneassignments, to Loewe-Radio, Inc., a cor- 'poration' of New York Application-February 19, 1938, Serial No; 191,450

In Germany February 24,1937

6 Claims.

If a largetuning range of the received signals and at the same time wide-band amplification is required of anultra-short wave receiver, difiiculties are encountered when employing the normal oscillatory circuit arrangements; The un- There is accordingly obtained in the series connectionwith a given Width of bandan amplification which is five times as great, as it is possible to employ one-fifth of the. damping. 1

There-will be recognised from. the examples avoidable inter-electrode capacities and the ingiven 'the obvious fundamentalsuperiority of the herent earth capacities call in the case of a series connection of Cl and Ca as compared with given wave range fora comparatively large cathe parallel connection. At the. same timehowpacity of the rotating plate condenser. These ever, it will also be recognised that 'the receiving V two in parallel lead to a very small coil in the range, 1. e. the ratio w case of a given Wavelength. This results in a A 10 large e m g. is equally poor in both cases. Moreover the series connection hasat the same time the particu- M in a small oscillation resistance. It is accord- 'lar' dsadvantage a tuning curve varies mgqy necessary to perform Strong damping only in lagging fashion-with the angle of rotapoor amplification is obtained. In order to rem9 w lqnger Wavesduce this detrimental effect the applicant has al- The mventlon W111 le understood ready proposed previously-to reduce the working way of examples shown 1n the accompanying 20 capacity by a series connection'of the tuning w w er v condenser Ca with the inherent capacity Ci of and 3'Sh0W the undamental two a preeding tube The Working capacity is then circuit arrangement of parallel connection (Fig. 1 always smaller than C1. The coil .L is'accord and 'senes 2 and 3) already above ingly considerably larger. The following exam- Ff l 1 25 p18 serves f explanation; Figs. fl-5 show exemplary embod ments of the i present invention. Ca rotating plate condenser with a range of The circuit ystem asshown-in-Fig. 3 avoids 5-25 cm. the disadvantage above mentioned'whilst the am- Ci=l0 'plification advantages of the series connection In case of parallel connection the maximum are maintained. In this circuit system there are 7 p y amounts t0 v employed two rotating plate condensers Cal and Cnm= Cm" and the minimumcapacity' Caz, which are coupled together and are varied in thesame sense. Cal is parallel to Cl. The C =15 cm. condenser Ct is a trimmer. The condenser Ca'l 85 is in parallel with the inherent tube capacity C1, 2'

332: 455:1 5 ,and these two capacities together are in; series mi with the tuning condenser Ca2. I1 both tuning The tuning range of the circuit arrangement c ldeligers Ca have1 (a rgngefioft c qfip is accordingly very small. an 1 11S 38am e e 60 lve'capacl Y 40 In the case of'series connection the detrimental 311191130 the c011 amounts to p working capacity is much smaller, as v ratio of the receiving range C'mm=3.2 cm. 41:; I v cmaxzrl .The'maximum capacity in the case .of the long- .45 h tuning lange, therefore, is est ave amounts to merely 15 as comparedwith "45 1/ 35, in the usual circuit system according toFig. l. 1 The oscillation resistance, therefore, although i. e. is equally as'small. For a given'wave length, not so good, is 'still'more than twice ase as however, the coil is five times as large. The 05- in 1 .50 cillation resistance equals I With tuning condensers of cm. tuning ranges L are obtained of approximately 1:2.6, i. e. a'very useful value. The tuning curve of the circuit systemwith double condenser according to the inin the series connection is accordingly also five vention already closely'approaches to a straight times as large as in the :parallel connection. line in the case of circular plate condensers. :55

The flattening towards the longer tuning waves, which represents an appreciable disadvantage in the simple series connection according to Fig. 2, is in this case eliminated.

The damping of the tuning circuit formed by L and C111, 032 takes place by a damping resistance R parallel to the coil. The feeding of the grid or anode circuits with. the bias can be advantageously effected at the centre of the coil L via the choke D1. This point is efiectively at earth potential for the high frequencies.

The trimming of the circuit system is particularly simple. There is provided merely one trimmer Ct for tuning the inherent tubecapacities'. In the case of predetermined values for Ca. and L, which are always the same, there is then obtained an ideal unison of several circuits by increasing by means of Ct the too small associated inherent capacities C1 to the greatest value oc-- curring in the circuit system. The frequency curves then exactly coincide. In particular it is then possible to unite two circuits of this kind to form a band'filter. e

In Fig. 4 there is shown as an embodiment of the present invention a band filter circuit of this character employed as intermediate coupling between two tubes V1 and V2. In this case, generallyspeaking, the damping resistances R parallel to the coils L can be omitted, since a coupling resonance effect may be produced thus effecting a natural widening of the receiving frequency curve. In the anode circuit of valve V1, 'coil L1, tuning condensers Cal and C82 are connected in series and all this series connection in parallel to the anode-cathode pathof valve V1. The capacity Cm (so called trimmer) connected in parallel to condenser C92 is used for adjusting unison. In similar manner the grid circuit of the associated valve V2 is connected. L2 is the coupling coil connected in series with the tuning condensers Cgl and 2 and'this whole series connection is in parallel to the grid-cathode path of valve V2. By the capacity Ctg which is connected in parallel to C 2-the unison of the circuit is adjusted.

In Fig. there is set forth a special structural embodiment of the tuning condenser Ca in combination with a trimmer Ct. As will be recognised from Figs. 3 and 4, the two rotors of the two condensers Cal and C212 may be electrically connected together in the circuit according to the invention. It is accordingly possible to place at least the two condenser halves of a circuit and also even compound condensers of coupled circuits on a common metallic shaft 0, as shown in Fig. 5. According to the invention there mayv be fitted on this shaft metallic intermediate discs S1, S2 and S3 connected with the shaft. Ral, R52 and Rgl, RgZ are the rotor plates of the single tuning capacities C111, Ca2 and Cgl and CgZ (shown in Fig. 4) The discs S1 and S3 separate the two stator halves of the two single circuits. The stray capacity parallel to the coil is thus divided in each case into two capacities to earth, i. e. parallel to the tuning parts. If the screening discs S1 and S3 in particular are made to be shiftable on the shaft, as indicated by an arrow in Fig. 5, the capacity Ct shown. in broken lines between the stator assembly on the anode side and this disc acts simultaneously as trimmer. In place thereof there may, of course, also be employed a separate small condenser Ct, which is connected with one electrode to earth and in consequence can be readily adjusted without de- 1' tuning the circuit system as shown in Fig. 5 in the tuning circuits according to the invention with a local oscillator, which in the case of superheterodyne receiversshould then traverse in constantfrequency spacing the same receiving range with a tuning curve as analogous as possible. It has been found, and will also be readily recognised, that the circuit system according to the invention does not essentially require to be employed for a local oscillator of this character, and that it is possible to use for this oscillator the usual parallel connection of C and L or other known circuit systems. The reasons leading up to the circuit system according to the invention relate purely to amplification, and fundamentally cease to exist in respect to a local oscillator. According, therefore, to the invention, a local oscillator having rotating plate condensers with the same form of plate, but with parallel connection' of C andL and correspondingly greater can be mechanically coupled with advantage with amplifying circuits and band filter systems of the compound condenser connections according to the invention as shown in Figs. 4 to 5. The tuning curves are completely identical in their form if the plate section is the same. The trimming of the local oscillator to the correct receiving range is a problem which'has become a matter of course in the present-day radio art.

I claim:

1. In an amplifier arrangement two tunable coupling circuits for coupling two successive amplifier stages for effecting wide-band amplification, more particularly for ultra-short wave circuits, each of said coupling circuits consisting of a valve, a coil and a tunable capacity, said tunable capacity being divided into two single condensers which are varied synchronously and connected in series with said coil, one of said condensers beingconnected in parallel to the valve and having connected in parallel a special condenser of adjustable capacity with respect to earth, said coils being inductively coupled with each other in such manner that a wide-band is amplified, said first tunable circuit being connected in'parallel to one of said stages, said second tunable circuit being connected in parallel to the grid-cathode path of the associated valve.

2. In an amplifier arrangement two tunable coupling circuits for coupling two successive amplifier stages for effecting wide band amplification, more particularly for ultra-short wave circuits, each of said coupling circuits consisting of a valve, a coil and a tunable capacity, said tunable capacity being divided into two single con- .densers which are varied synchronously and connected in series with said coil, one of said condensers being connected in parallel to the valve and having connected in parallel a special condenser of adjustable capacity with respect to earth, said'coils being inductively coupled with each other in'suchmanner that a wide-band is amplified, said first tunable circuit being connected in parallel to one of said stages, said second tunable circuit being connected in parallel to the grid-cathode path of the associated valve, the rotors of said tunable condensers being mounted on a common earthed shaft, the stators being disposed in axial direction in relation to each other and screened one from another by an intermediate earthed sheet.

3. In an amplifier arrangement two tunable coupling circuits for coupling two successive amplifier stages for effecting wide-band ampli fication, more particularly for ultra-short wave circuits, each of said coupling circuits consisting of a valve, a coil and a tunable capacity, said tunable capacity being divided into two single condensers which are varied simultaneously and connected in series with said coil, one of said condensers being connected in parallel tothe valve, said coils being inductively coupled with each other in such manner that a wide-band is amplified, said first tunable circuit being connected in parallel to one of said stages, said second tunable circuit being connected in parallel to the grid-cathode path of the associated valve,

the rotors of said tunable condensers being mounted on a common earthed shaft, the stators being disposed in axial direction in relation to each other and screened one from another by an intermediate earthed sheet, said intermediate sheet being axially shiftable for the purpose of tuning additionally the inherent capacity of the circuit arrangement.

4. In an amplifier arrangement two tunable coupling circuits for coupling two successive amplifier stages for effecting wide-band amplifie' cation, more particularly for ultra-short wave circuits, each of said coupling circuits consisting of a valve, a coil and a tunable capacity, said tunable capacity being divided into two single condensers which are varied synchronously and connected in series with said coil, one of said condensers being connected in parallel to the valve and having connected in parallel a special condenser of adjustable capacity with respect to earth, said coils being inductively coupled with each other in such manner that awide-band is amplified, said first tunable circuit being connected in parallel to one of said stages, said second tunable circuit being connected in par' allel to the grid-cathode path of the associated valve, the rotors of said tunable condensers being mounted on a common earthed shaft, the

stators being disposed in axial direction in relation to each other and screened oneirom another by a circular disc conjointly rotating on the shaft, and being axially shiftable for the purpose of tuning additionally the inherent capacity of the circuit arrangement. a

5. In an amplifier arrangement two tunable coupling circuits for coupling two successive amplifier stages for efiecting wide-band amplification, more particularly for ultra-short wave circuits, each of said coupling circuits consistin of alvalve, a coiland a tunablecapacity, said tunable capacity being dividedinto two single condensers which are varied synchronously and.

connected in series with said coil, one of said condensers being connected in parallel to the valve and having connected in parallel a special condenser of adjustable capacity with respect to earth, said coils being inductivelycoupled with each other in such manner that a wide-band is.

amplified, said first tunable circuit being connected in parallel to one of said stages, said second tunable circuit being connected in parallel to the grid-cathode path of the associated valve,

both said coupling circuits being enclosed by an earthed screening casing.

6. In an amplifier arrangement two tunable coupling circuitsv for. coupling twosuccessive amplifier stages for effecting wide-band amplification, more particularly for ultra-short wave circuits, each of said coupling circuits consisting of a valve, a coil and a tunable capacity, said tunable capacity being divided into two single condensers which are varied synchronously and connected in series with said coil, one of said condensers being connected'in parallel to the valve, said coils being inductively coupled with each other in such manner that a'wide-band :is

amplified, said first tunable circuit being conlation to each other andscreened one fromanother by an intermediate earthed sheet, said intermediate sheet being axially ,shiftable for the purpose of tuning additionally ithe inherent capacity of the circuit arrangement, both saidcoupling circuits being enclosed by an earthed screening casing.

. KURT SCI-ILESINGER.

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